Timing modulation



June 26, 1945. e. L. USSELMAN TIMING MODULATION Filed April so, 1943 M .m+ Rm w s d E. NE 4 6 7% ATTORNEY Patented June 26, 1945 TIMING MODULATION George L. Usselman, Port Jeflerson, N. E, asslgnor to Radio Corporation of America, a corporation oi' Delaware Application April 30, 1943, Serial No. 485,102

14 Claims.

This application discloses a. new and improved means for generating wave energy, stabilizing the frequency of the wave energy, and modulating the timing of the generated wave energy in accordanc with the signals.

An object of the present invention is wave length modulation wherein oscillations of substantially constant n can frequency are generated and wherein the timing or length of the oscillations is modulated in accordance with signals.

A further object of the present invention is generation of oscillations of substantially constant mean frequency and of substantially constant amplitude or strength and modulation of said generated oscillations as to timing or wave length substantially linearly in accordance with signals without materially modulating the amplitude thereof.

The above objects are attained in accordance with the present invention by generating oscillations in a tube having electrodes coupled in regenerative circuits including a piezo-electric crystal, the natural period of resonance of which is the same as the mean frequency of the oscillations when modulated. The crystal has associated therewith a parallel tuned reactive circuit having two branches, one of which is capacitive and the other of which is inductive, with the parallel circuit tuned to resonance at the crystal frequency. The two branches of the resonant circuit or portions thereof are shunted by variable resistances which are varied dlflerentially in accordance with the signals'to thereby alternately increase and decrease th reactances 01' the respective branches and to alternately change the reactance associated with the crystal to thereby modulate the timing or length generated.

In a preferred modification the variable resistances comprise the internal impedance of electron discharge devices.

1 Additional objects and the manner in which they are attained will appear from the following detailed description of the invention.

In describing my invention in detail reference will be made to the attached drawing, wherein the two figures illustrate schematically the circuits of a wave length modulation system arrangement in accordance with my invention.

In Fig. 1, ill is an electron discharge device having a main anode l2 coupled electronically to the oscillation generating electrodes and coupled to a parallel tuned circuit l 4 from which the timing modulated oscillations may be supplied to frequency multipliers and/ or amplifiers and/or amof the oscillationsplitude limiters or more directly to utilization means. The oscillation generating electrodes comprises an electrode 18 serving as an anode and coupled to one terminal of the piezo-electric crystal x, the other terminal 01 which is connected to a controlling electrode It. The electrode l2, l6 and II are supplied with appropriate operating potentials as shown, with the sources of supply shunted by bypassing condensers BP. In this generator oscillations are generated by virtue of the fact that the generated potentials at the terminals or the crystal x are subtantially 180 out of phase on the electrodes l8 and it, while the cathode of the tube is at a generated potential intermediate the said two potentials. The oscillations generated are of a frequency substantially equal to the natural frequenc of operation of crystal X, this in turn depending upon the dimensions thereof, the holder capacity, etc. A slight or Vernier adjustment of the frequency or operation oi. the crystal may be made by adjustment of the condenser 24.

The resonant circuit, comprising a capacitive branch C l and C2 and an inductive branch L is coupled between one terminal of the crystal X and ground through a coupling condenser 28. The circuit L, Cl, C2 is'tuned to the mean frequency of operation of the oscillation generator as determined by crystal X. In tuning this circult to resonance at said frequency, the choke coil CH through which the anode potential issupplied to the modulator tubes 30 and 32, is not taken into account, since its inductance is approximately one-quarter wave length of the operating frequency and therefore has substantially no eiiect on the tuned circuit. The modulator tube 30 has its anode tapped to a point on the inductive branch L, while the modulator tube 32 has its anode tapped to a point on the capacity potentiometer, in the capacitive branch in the arrangement shown between condensers Cl and C2. The control grids of the tubes 30 and 32 are differentially modulated by signals from source 38 operating through transformer 38. The control grids are biased by connections as shown, while the anodes derive their direct current potential by way of choke CH and a portion of the inductive branch L. The source of direct current is also bypassed by condenser 13?.

The crystal controlled oscillator circuit includes the control grid i8 and the third or anode grid I6 of the tube Ill and the crystal X itself and, if desired, condenser 24. The output circuit I4 is electronically coupled to the oscillator through the anode II of tube ID. The resistors l1 and i8 supply direct current potentials to the control grid I8 and anode grid ll, respectively. It may be noted that as to the oscillator circuit the only reactance therein is the crystal X and, if desired, the capacity 24. The coupling condenser 28 should be large enough to provide the required coupling, but not large enough to permit the crystal to lose control of the operation.

The reactance L, Cl and C2 of the modulator, however, is connected between one crystal electrode and ground and this circuit is tuned to resonance at the crystal frequency and being a par,- allel circuit is of high impedance to oscillations of the generated'frequency. This circuit then is in effect a pure resistance connected between an electrode of the crystal and ground and the oathode of tube iii. If a variable resistance or impedance is tapped across a portion of either branch of the parallel circuit the tuned circuit becomes a variable impedance with a reactive component which varies with variations of the impedance.

As to this modulator circuit, the resistance of tube 30 is connected in shunt to an adjustable portion of L, while the resistance of tube 22 is connected in shunt to an adjustable portion of the capacity potentiometer Cl, C2. The shunting impedances comprising tubes 20 and 82 in the unmodulated state are considered when setting the tuning of L, Cl, C2, as is the wave length shunting choke CH. The bias on the grids of tubes 30 and 32 (in the absence of modulation) is such that the circuit L, Cl, C2 is at parallel resonance to the frequency of the crystal which is the carrier frequency.

When tube 30 is conductive and tube 32 is less conductive a portion of the inductive branch is shunted by a low impedance while a portion of the capacity of the branch Cl, C2 is shunted by a high impedance. This reduces the inductive reactance of L and increases the capacitive reactance of Cl, C2 and the parallel resonant circuit tunes to a higher frequency and the crystal has connected thereto an inductive reactance, thereby increasing the frequency of operation thereof. When tube 32 is conductive and tube 30 is less conductive the impedance of tube 22 is low while the impedance of tube 20 is high and the inductance of L assumes a higher value, while the capacity of the branch Cl, C2 is increased and the reactance connected with the crystal X is capacilations generated decreases. The conductivity of tubes 30 and 22 or the resistance thereof is diife'rentially modulated in accordance with signals from source 20.

A feature of this improved form of modulation resides in the fact that since the modulation is differential the effective resistance across the parallel tuned circuit remains substantially constant during modulation and little or no amplitude modulation of the generated oscillations is produced while timing modulation is being accomplished.

In the modification of Fig. 1, the resonant circuit CI, C2, L is, as will be seen from the above description, single ended with respect to the crystal x.

In the modification of Fig. 2, the resonant cir-,

cult is double ended. By this it is meant that both ends thereof are coupled to the crystal electrodes, one end being coupled as in Fig. 1 by coupling condenser 28 and the other end being coupled to the other crystal electrode by coupling condenser 28' so that the resonant circuit shunts the crystal. Points intermediate the ends of the capacitive leg C, Cl, C2 are connected to ground and the cathode of tube III. In this modification C and Cl are equal in capacity to-C2. The crystal X is the sole reactance in the oscillation generating circuit and the output circuit I4 con- I nected to the anode III is tuned by its distributed capacity only, i; e., is self-resonant. The condensers 2| and 28 between the crystal and the modulation circuit should not be too large or the crystal will lose control of the operation. The arrangement of Fig. 2 is otherwise substantially as in Fig. 1. while the operation thereof is also substantially as given above in connection with Fig. 1.

I claim:

1. In a timing modulation system, an electron discharge device having oscillation generating electrodes coupled in a regenerative oscillation generating circuit including a crystal having at least two electrodes whereby oscillations are generated in said device and circuits, a circuit parallel tuned to resonance at the frequency of operation of said generator as determined by said crystal, said tuned circuit having an inductive branch and a capacitive branch, a coupling between said resonant circuit and an electrode of said crystal, 9, variable impedance in shunt to a portion, at least, of said inductive branch; a variable impedance in shunt to a portion, at least, of

said capacitive branch, and means for varying tive in nature so that the frequency of the oscil- I said impedances differentially in accordance with signals to set up in the crystal a reactive component which changes in accordance with the said signals.

2. In a timing modulation system, an electron discharge tube having oscillation generating electrodes coupled in oscillation generating circuits including a crystal having two terminals, one of which is connected to an anode like electrode of said tube, and the other of which is connected to a control electrode of said tube, whereby oscillatins are generated in said tube, a parallel circuit tuned to resonance at the frequency of operation of said generator as fixed by said crystal, said tuned circuit having an inductive branch and a capacitive branch, a coupling between said resonant circuit and said crystal, a variable impedance in shunt to a portion, at least, of said inductive branch, at variable impedance in shunt to a portion, at least, of said capacitive branch, and means for varying said impedances differentially in accordance with signals.

3. In a timing modulation system, an electron discharge tube having a control electrode, an anode and a cathode coupled in oscillation generating circuits including a crystal having two terminals, one of which is connected to said anode of said tube, and the other of which is connected to said control electrode of said tube, whereby oscillations are generated in said tube, a circuit parallel tuned to resonance at the frequency of operation of said generator as controlled by said crystal, said tuned circuit having an inductive branch and a capacitive branch, a coupling between said resonant circuit and one terminal of said crystal, 3. coupling between the other terminal of said resonant circuit and the cathode of said tube. a variable impedance in shunt to a portion, at least, of said inductive branch, a variable impedance in shunt to a portion, at least, of said capacitive branch, and means for varying said impedances differentially in accordance with signals.

4'. In a timing modulation system, an electron minal of said resonant circuit and the other electrode of said crystal, a variable impedance in shunt to a portion, at least, of said inductive branch, a variable impedance in shunt to a portion, at least, of said capacitive branch, and connections for varying said impedances diiferentially in accordance with signals to set up across the crystal a, reactive component which changes in accordance with the said signals.

5. In a signalling system, an electron discharge 4 tube having oscillation generating electrodes coupled in oscillation generating circuits including a crystal connected between two electrodes of said tube, whereby oscillations are generated in said tube, a parallel tuned circuit having an inductive branch and a capacitive branch, 9, coupling between said parallel tuned circuit and said crystal, a variable impedance in shunt to a portion, at least, of said inductive branch, a variable impedance in shunt to a portion, at least, of said capacitive branch, the values of said variable im pedances and the reactances of said inductive branch and capacitive branch being such that the parallel tuned circuit is tuned substantially to the crystal frequency, means for varying said impedances diiferentially in accordance with control potentials, and an output circuit coupled to said oscillation generator circuits.

6. In a signalling system, an electron discharge tube having a control electrode, an anode and a cathode coupled in oscillation generating circuits including a crystal having two terminals, one of which is connected to said anode of said tube, and the other of which is connected to said control electrode of said tube, whereby oscillations are generated in said tube, a parallel tuned circuit having an inductive branch and a capacitive branch, a coupling between said parallel tuned circuit and one terminal of said crystal, a coupling between the other terminal of said parallel tuned circuit and the cathode of said tube, a variable impedance in shunt to a portion, at least, of said inductive branch, a variable impedance in shunt device having oscillation generatingeiectrodes coupled in a regenerative oscillation generating circuit including a crystal having at least two electrodes whereby oscillations are generated in said device and circuits, a parallel tuned circuit having an inductive branch and a capacitive branch, a coupling between one terminal of said parallel'tuned circuit and an electrode of said crystal, a coupling between the other terminal of said parallel tuned circuit and the other electrode of said crystal, a variable impedance in shunt to a portion, at least, of said inductive branch, a variable impedance in shunt to a portion, at least, of

said capacitive branch, the values of said variable impedances and the reactances of said inductive branch and capacitive branch being such that the parallel tuned circuit is timed substantially to the crystal frequency, and connections for varying said impedances differentially in accordance with control potentials to set up across the crystal a reactive component which changes in accordance with the said control potentials.

8. A system as recited in claim 1, wherein said variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled differentially in accordance with signals to varythe said impedances.

variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled diiferentially' in accordance with control potentials to vary the said impedances.

10. A system as recited in claim 3, wherein said variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled differentially in accordance with control potentials to vary the said impedances.

11. A system as recited in claim 4, wherein said variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled differentially in accordance with control potentials to vary the said impedances.

12. A system as recited in claim 5, wherein said variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled diiferentially in accordance with control potentials to vary the said impedances.

13. A system as recited in claim 6, wherein said variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled differentially in accordance with control potentials to vary the said impedances.

-14. A system as recited in claim 7, wherein said variable impedances comprise the impedance between electrodes in electron discharge tubes and wherein the gains of the tubes are controlled differentially in accordance with control poten tials to vary the said impedances.

GEORGE Io. UBBEIMAN. 

